A known electric actuator transmits a drive torque of an electric motor to a rotatable shaft of a throttle valve (a throttle shaft), as disclosed in, for example, JP2008-019825A (corresponding to US2008/0011269A1). As shown in FIGS. 11A and 11B, one such electric actuator includes a throttle gear 102, a return spring 103, and an installation member 104. The throttle gear 102 transmits a drive torque of the electric motor to a throttle shaft 101 of a throttle valve to rotate the throttle shaft 101. The return spring 103 generates a resilient force relative to the throttle gear 102 to urge the throttle shaft 101 in a rotational direction (valve closing side) to rotate a rotational position of the throttle shaft 101 to an initial position. The return spring 103 is installed between the throttle gear 102 and the installation member 104.
With reference to FIG. 11A, one axial end portion of the throttle shaft 101 is fitted into a fitting hole 105 of the throttle gear 102. When the one axial end portion of the throttle shaft 101 projects through the fitting hole 105, the one axial end portion of the throttle shaft 101 is fixed to a center portion of the throttle gear 102 by plastically deforming a projected tip of the one end portion of the throttle shaft 101, which projects from the fitting hole 105, as shown in FIG. 11B.
A spring guide 106 and a movable hook 107 are formed in the throttle gear 102. The spring guide 106 is configured into a cylindrical tubular form and supports a radially inner side of a coil of the return spring 103. A first end portion 111 of the return spring 103 is engaged to the movable hook 107.
A spring guide 108 and a stationary hook 109 are formed in the installation member 104. The spring guide 108 is configured into a cylindrical tubular form and supports the radially inner side of the coil of the return spring 103. A second end portion 112 of the return spring 103 is fixed to the stationary hook 109.
In the above described electric actuator, at the time of assembling the throttle gear 102 and the return spring 103 to the throttle shaft 101, first of all, the first end portion 111 of the return spring 103 is installed to the movable hook 107 of the throttle gear 102, and the coil of the return spring 103 is placed to surround the spring guide 106. Thereby, the return spring 103 is set to the throttle gear 102.
Thereafter, as shown in FIG. 11A, in a state where the coil of the return spring 103 is twisted by an initial set angle, and the throttle gear 102 is urged against, for example, a full-closing side stopper, the one axial end portion (a fitting portion 110) of the throttle shaft 101 is fitted into the fitting hole 105 of the throttle gear 102.
Next, in order to fix the throttle gear 102 to the fitting portion 110 of the throttle shaft 101, as shown in FIG. 11B, the fitting portion 110 is fixed to the throttle gear 102 by plastically deforming the tip of the fitting portion 110, or the fitting portion 110 is securely press fitted into the fitting hole 105. In this way, the gear assembly is assembled to the installation member 104.
However, in the above-described electric actuator, the assembling work of the gear assembly relative to the installation member 104 is very complicated, so that the efficiency of the assembling work is deteriorated.
Furthermore, at the spring guides 106, 108, which guide the radially inner side of the coil of the return spring 103, a boundary (a gap S) is intrinsically generated between the throttle gear 102 and the installation member 104. Thus, wearing may cause generation of an undesirable play between the spring guides 106, 108, or a wire of the coil of the return spring 103 may possibly enter the gap S to cause malfunction of the electric actuator.